The present invention relates to a polymer light emitting device (hereinafter referred to as an xe2x80x9cpolymer LEDxe2x80x9d).
An inorganic electroluminescence device using an inorganic fluorescent substance as a light emitting material (which may hereinafter referred to as an xe2x80x9cinorganic EL devicexe2x80x9d) has been used, for example, as a flat light source for back light or a display device such as a flat panel display and the like, however, high A.C. voltage has been required to emit light.
Recently, Tang et al. manufactured an organic electroluminescence device (hereinafter referred to as an xe2x80x9corganic EL devicexe2x80x9d) having a double-layer structure, comprising a laminate of a light emitting layer made of an organic fluorescent dye and a layer of an organic charge transporting compound generally used, for example, as a photosensitive material for electrophotography (JP-A-59-194393). Since the organic EL device has a feature that emission of light of various colors can be easily obtained, in addition to low-voltage driving and high luminance, in comparison with the inorganic EL device, various attempts for device structure, organic fluorescent dye and organic charge transporting compound have been reported (Jpn. J. Appl. Phys., Vol. 27, page L269 (1988); and J. Appl. Phys., Vol. 65, page 3610 (1989)).
The polymer LED using a polymeric light emitting material, other than the organic EL device mainly using low-molecular weight organic compounds, has been proposed in WO9013148, JP-A-3-244630, Appl. Phys. Lett. Vol.58, page 1982 (1991) and the like. In the Examples of WO9013148, there is disclosed that a poly(p-phenylenevinylene) thin film converted into a conjugated polymer is obtained by forming a film of a soluble precursor on an electrode and then subjecting it to a heat treatment, and a device using the same.
Furthermore, JP-A-3-244630 discloses conjugated polymers having a feature that the conjugated polymers themselves are soluble in solvents and require no heat treatment. Also, in Appl. Phys. Lett. Vol.58, page 1982 (1991), there are described polymeric light emitting materials, which are soluble in solvents, and polymeric LEDs made by using the same.
JP-A-3-273087 discloses a polymer LED formed by laminating a light emitting layer of a polymeric light emitting material and a hole transporting layer of a conjugated polymer. In case of a polymer LED, a device having high light emitting efficiency can also be obtained by providing a laminated structure. However, there has been required an organic EL device having a sufficient long-term stability, wherein a decrease in luminance and an increase in voltage on driving are smaller than those of these devices.
A method of elongating the lifetime of a light emitting device is proposed, for example, in WO94/06157, JP-A-8-231951 and the like, particularly with respect to an organic EL device made by deposition of a low-molecular-weight material. WO94/06157 discloses that, when a small amount of distyrylalylene derivative is added to a light emitting layer or a hole transporting layer, it functions as an charge injection assistant, and the lifetime of the device is elongated. JP-A-8-231951 discloses that a device having a elongated lifetime can be obtained by using a light emitting layer made by adding a condensed polycyclic aromatic compound to a diamine derivative.
On the other hand, regarding the polymer LED, since an organic layer can be easily formed by coating, it is advantageous to increase the area and to reduce the cost compared with the case where a low-molecular-weight material is deposited. It is considered that the mechanical strength of the film is also excellent by virtue of polymer, but elongation of the lifetime is unsatisfactory. That is, an improvement in stability on driving is required in the polymer LED.
An object of the present invention is to provide a long-life polymer light emitting device having excellent stability on driving.
Under these circumstances, the present inventors have intensively studied. As a result, the present inventors have found that a long-life polymer light emitting device having excellent stability can be obtained without deteriorating the feature such as luminance, light emitting efficiency and the like, by adding a specific organic compound to a charge transporting layer. Thus, the present invention has been accomplished.
That is, the present invention relates to a polymer light emitting device at least having a light emitting layer containing a polymeric fluorescent substance and a charge transporting layer provided adjacent to the light emitting layer between electrodes consisting of a pair of an anode and a cathode, at least one of which electrode is transparent or semitransparent, wherein said polymeric fluorescent substance contains one or more kind of repeating units represented by the following formula (1), the sum of the repeating units being not less than 50% by mol based on the total repeating units, and has a number-average molecular weight of 103 to 107 in terms of polystyrene
xe2x80x94Ar1xe2x80x94CR1xe2x95x90CR2xe2x80x94xe2x80x83xe2x80x83(1)
(wherein Ar1 represents an arylene group having 4 to 20 carbon atoms taking part in a conjugated bond, or a heterocyclic compound group having 4 to 20 carbon atoms taking part in a conjugated bond; and R1 and R2 independently represent a group selected from the group consisting of hydrogen, an alkyl group having 1 to 20 carbon atoms, an aryl group having 6 to 20 carbon atoms, a heterocyclic compound group having 4 to 20 carbon atoms and a cyano group), and said charge transporting layer contains an organic compound satisfying the following conditions 1 and 2 in an amount of from 1 to 70% by weight
EOX2xe2x88x920.15xe2x89xa6EOX1xe2x89xa6EOX2+0.10xe2x80x83xe2x80x83(condition 1)
xcexedge2xe2x88x9230xe2x89xa6xcexedge1xe2x89xa6xcexedge2+20xe2x80x83xe2x80x83(condition 2)
(wherein EOX1 and xcexedge1 respectively represent an electrochemically determined oxidation potential and an absorption edge wavelength of an absorption spectrum of said organic compound; EOX2 and xcexedge2 respectively represent an electrochemically determined oxidation potential and an absorption edge wavelength of an absorption spectrum of said polymeric fluorescent substance used in said light emitting layer; and the unit in the condition 1 is V and the unit in the condition 2 is nm).
As the structure of the polymer LED of the present invention, a light emitting layer containing a polymeric fluorescent substance and a charge transporting layer containing the organic compound (A) are laminated.
For example, the structures of the following (a) to (e) are shown.
(a) Anode/Hole transporting layer (Organic compound(A))/Light emitting layer/Cathode
(b) Anode/Hole transporting layer (Organic compound (A))/Light emitting layer/Electron transporting layer/Cathode
(c) Anode/Light emitting layer/Electron transporting layer (Organic compound (A))/Cathode
(d) Anode/Hole transporting layer/Light emitting layer/Electron transporting layer (Organic compound(A))/Cathode
(e) Anode/Hole transporting layer (Organic compound(A))/Light emitting layer/Electron transporting layer (Organic compound(A))/Cathode
In the above, the symbol xe2x80x9c/xe2x80x9d represents lamination, and xe2x80x9c(Organic compound(A))xe2x80x9d represents that the organic compound(A) is contained in the layer.
Two or more light emitting layers, hole transporting layers and electron transporting layers may be independently used and, furthermore, a buffer layer may be inserted into any of interfaces in order to improve the adhesion and prevent the interface from the mixing. The order and number of layers to be laminated and the thickness of each layer are not specifically limited, but can be appropriately used considering the light emitting efficiency and the lifetime of the device.
Furthermore, the present invention also includes the case where the organic compound (A) is contained in the charge transporting layer and, at the same time, contained in the light emitting layer in the above structure.
In the polymer LED of the present invention, the organic compound (A) added in the charge transporting layer will be described hereinafter. The organic compound (A) may be any one which satisfy the conditions 1 and 2. When the values of the electrochemically determined oxidation potentials of the organic compound (A) and a polymeric fluorescent substance used as a light emitting layer (EOX1 and EOX2 respectively) and the absorption edge wavelengths of the absorption spectrum (xcexedge1 and xcexedge2 respectively) are respectively very close each other, the conditions 1 and 2 are satisfied. That is, it is the case that where the difference between EOX1 and EOX2 is from xe2x88x920.15 to +0.10V and the difference between xcexedge1 and xcexedge2 is from xe2x88x9230 to +20 nm. When these conditions are satisfied, transfer of charge or energy would become easy between the organic compound (A) and the polymeric light emitting substance used in the light emitting layer.
As a specific method of determining the difference of the oxidation potential, the following electrochemical method can be used. That is, the cyclic voltammetry of the organic compound (A) and that of the polymeric fluorescent substance are conducted and potentials (oxidation potentials) at which the oxidation wave rise from the baseline are obtained to take the difference. Specifically, for example, first, a thin film is formed on a platinum electrode by dipping from a solution of the material to be measured. Then, cyclic voltammetry is conducted in an organic solvent containing a suitable supporting electrolyte, for example, in an acetonitrile solution of 0.1 N tetrabutylammonium tetrafluoroborate, using a platinum electrode coated with the material as a working electrode, using another uncoated platinum electrode as a counter electrode and using, for example, a silver/silver chloride electrode, a saturated calomel electrode, standard hydrogen electrode and the like as a reference electrode. When the material to be measured is easily dissolved in the solvent used as an electrolysis solution, the measurement may be conducted by dissolving this material in the electrolysis solution instead of coating the electrode. The concentration may be selected so that the oxidation wave can be easily detected.
At that time, various conditions such as sweep rate and sweep region of the potential are fixed during the measurement of any materials, for example, 50 mV/second as the sweep rate and xe2x88x92200 to 1200 mV (potential vs. silver/silver chloride electrode) as the sweep region are specified. For the resulting cyclic voltammogram, the potential of the intersecting point of the tangent line to the baseline and the tangent line to the rising portion of the oxidation wave may be determined with each material to take the difference.
On the other hand, to determine the difference between the absorption edge wavelengths of the absorption spectrum, the absorption spectra are measured and the wavelengths at which the absorption rises from the baseline are obtained to take the difference. Specifically, a thin film having a thickness of approximately 50 to 300 nm is formed on a quartz substrate by spin-coating from a solution of the material to be measured, thereby to obtain the absorption spectrum. For this spectrum, the wavelength of the intersecting point of the tangent line to the baseline and the tangent line to the rising portion of the absorption spectrum is regarded as the absorption edge wavelength. This may be determined with each material to take the difference.
The organic compound (A) is appropriately selected so as to satisfy the conditions 1 and 2 depending on the combination with the polymeric fluorescent substance used as a light emitting layer. The organic compound is, for example, an oligomer having repeating units, which are similar to or the same as those of the polymeric fluorescent substance used in a light emitting layer, and a low-molecular-weight compound having a condensed polycyclic aromatic compound group conjugated to similar or the same structure to the repeating unit and the like. In this case, it is preferable that the condensed polycyclic aromatic compound group contains three or more rings.
Particularly, in the case of having a structure of the repeating unit composed of the same skeleton as that of the polymeric fluorescent substance used in a light emitting layer in the molecule, that is, in the case of having one or more kinds of repeating units of a polymeric fluorescent substance used in a light emitting layer in a part of constituting units of the organic compound, it is likely to become similar energy state, so it is preferable. The polymeric fluorescent substance itself used in the light emitting layer also satisfies the conditions 1 and 2, but when the charge transporting layer is composed of a polymeric material, it is difficult to mix uniformly and phase separation arises sometimes. On the other hand, when the molecular weight of the organic compound (A) is very small, if the large amount of it is added, the film quality and film strength of the charge transporting layer are likely to becomes insufficient. Depending on the structure of the charge transporting material and the organic compound (A), the molecular weight of the organic compound (A) is preferably not more than 104 and not less than 5xc3x97102, and more preferably not more than 4xc3x97103 and not less than 103, in order to uniformly disperse into the charge transporting layer. For example, an oligomer containing from 3 to 7 of the repeating units represented by the above formula (1) on the average has a suitable molecular weight and, therefore, it can be preferably used.
Specific examples of the organic compound (A) include the compounds represented by the following formulas (2), (5) and (6). These organic compounds (A) may be used alone or in combination thereof. The content of the organic compound in the charge transporting layer is from 1 to 70% by weight based on the whole material contained in the layer. To obtain the sufficient effect, the larger the amount, the better. To maintain the film quality, the smaller the amount, the better. Therefore, the content of the organic compound in the charge transporting layer is preferably from 4 to 70% by weight, more preferably from 9 to 50% by weight, and particularly from 15 to 40% by weight.
A method of mixing the organic compound (A) in the charge transporting layer is not specifically limited, but is appropriately decided depending on the charge transporting layer to be used. For example, when the charge transporting material is a low-molecular-weight material, a co-deposition method is used as a vacuum depositing method and a method of mixing in a solution is used as a method of forming a film from a mixed solution with a polymeric binder. When the charge transporting material is a polymer, since film formation from a solution is general, a method of mixing to a solution is used.
Ar2xe2x80x94CR3xe2x95x90CR4xe2x80x94"Parenopenst"B"Parenclosest"xe2x80x94nAr3xe2x80x94CR5xe2x95x90CR6xe2x80x94Ar4xe2x80x83xe2x80x83(2)
In the formula, B is a divalent compound group represented by the following formula (3) or (4), a group obtained by combining one or more groups represented by (3), a group obtained by combining one or more groups represented by (4), or a group obtained by combining one or more groups represented by (3) with one or more groups represented by (4)
xe2x80x94Ar5xe2x80x94CR7xe2x95x90CR8xe2x80x94xe2x80x83xe2x80x83(3)
xe2x80x94Ar6xe2x80x94CR9xe2x95x90CR10xe2x80x94Ar7xe2x80x94CR11xe2x95x90CR12xe2x80x83xe2x80x83(4)
wherein Ar3, Ar5, Ar6 and Ar7 independently represent an arylene group having 4 to 20 carbon atoms taking part in a conjugated bond, or a heterocylic compound group having 4 to 20 carbon atoms taking part in a conjugated bond, but Ar6 and Ar7 are not the same; n is an integer of 0 to 10. In the case that B is represented by the formula (3), n is more preferably an integer of 2 to 6, and when B is represented by the formula (4), n is more preferably an integer of 1 to 3; Ar2 and Ar4 independently represent a condensed polycyclic aromatic compound group having 3 to 10 rings, or when n is 4 to 10, Ar2 and Ar4 independently represent an aryl group having 4 to 20 carbon atoms taking part in a conjugated bond, or a heterocylic compound group having 4 to 20 carbon atoms taking part in a conjugated bond; and R3, R4, R5, R6, R7, R8, R9, R10, R11 and R12 independently represent a group selected from the group consisting of hydrogen, an alkyl group having 1 to 20 carbon atoms, an aryl group having 6 to 20 carbon atoms, a heterocyclic compound group having 4 to 20 carbon atoms and a cyano group. 
wherein Ar12 represents a tetravalent aryl group having 4 to 20 carbon atoms taking part in a conjugated bond, or a heterocylic compound group having 4 to 20 carbon atoms taking part in a conjugated bond; Ar8 to Ar11 independently is selected from a condensed polycyclic aromatic compound group having 3 to 10 rings; R13 to R20 independently represent a group selected from the group consisting of hydrogen, an alkyl group having 1 to 20 carbon atoms, an aryl group having 6 to 20 carbon atoms, a heterocyclic compound group having 4 to 20 carbon atoms and a cyano group. 
wherein Ar16 represents a trivalent aryl group having 4 to 20 carbon atoms taking part in a conjugated bond, or a heterocylic compound group having 4 to 20 carbon atoms taking part in a conjugated bond; Ar13 to Ar15 independently is selected from a condensed polycyclic aromatic compound group having 3 to 10 rings; and R21 to R26 independently represent a group selected from the group consisting of hydrogen, an alkyl group having 1 to 20 carbon atoms, an aryl group having 6 to 20 carbon atoms, a heterocyclic compound group having 4 to 20 carbon atoms and a cyano group.
Specific examples of Ar3,Ar5,Ar6 and Ar7 include a divalent group or a derivative thereof containing benzene, pyridine, pyradine, pyrimidine, pyridazine, naphtalene, anthracene, thiophene, fluorene, furane, quinoline, quinoxaline, pyrene, peryrene, phenanthrene, etc. or a divalent group combining thereof. Among them, benzene, naphtalene, anthracene, fluorene and pyrene are preferable.
Specific examples of Ar12 include a tetravalent group or a derivative thereof containing benzene, pyridine, pyradine, pyrimidine, pyridazine, naphtalene, anthracene, thiophene, fluorene, furane, quinoline, quinoxaline, pyrene, peryrene, phenanthrene, etc. or a tetravalent group combining thereof. Among them, benzene, naphtalene, anthracene, fluorene and pyrene are preferable.
Specific examples of Ar16 include a trivalent group or a derivative thereof containing benzene, pyridine, pyradine, pyrimidine, pyridazine, naphtalene, anthracene, thiophene, fluorene, furane, quinoline, quinoxaline, pyrene, peryrene, phenanthrene, etc. or a trivalent group combining thereof. Among them, benzene, naphtalene, anthracene, fluorene and pyrene are preferable.
Specific examples of a condensed polycyclic aromatic compound group represented by Ar2,Ar4,Ar8xcx9cAr11 or Ar13xcx9cAr15 include a divalent group or a derivative thereof containing anthracene, fluorene, pyrene, peryrene, coronene, naphtacene, phenanthrene, and so on. Among them, anthracene, fluorene, pyrene, peryrene and phenanthrene are preferable.
Ring number of condensed polycyclic aromatic compound is defined to be the number of all rings containing the condensed ring. For example, ring number of anthracene is 3, that of fluorene is 3, that of pyrene is 4, that of peryrene is 5, and so on.
In the case that n in the formula (2) is 4 to 10, specific examples of Ar2 or Ar4 include a divalent group or a derivative thereof containing benzene, pyridine, pyradine, pyrimidine, pyridazine, naphtalene, anthracene, thiophene, fluorene, furane, quinoline, quinoxaline, pyrene, peryrene, phenanthrene, etc. or a divalent group combining thereof. Among them, benzene, naphtalene, anthracene, fluorene and pyrene are preferable.
In the case that R3xcx9cR26 are not hydrogen or a cyano group, the alkyl group having 1 to 20 carbon atoms is exemplified by methyl group, ethyl group, propyl group, butyl group, pentyl group, hexyl group, heptyl group, octyl group, decyl group, lauryl group, etc. Among them, methyl group, ethyl group, pentyl group, hexyl group, heptyl group and octyl group are preferable.
The aryl group having 6 to 20 carbon atoms is exemplified by phenyl group, 4-C1-C12 alkoxyphenyl groups (C1-C12 refers to 1 to 12 carbon atoms, hereinafter referred to the same), 4-C1-C12 alkylphenyl groups, 1-naphtyl group and 2-naphtyl group and so on.
The heterocyclic compound group having 4 to 20 carbon atoms is exemplified by 2-thienyl group, 2-pyrrolyl group, 2-furyl group and 2-, 3- or 4-pyridyl group and so on.
Furthermore, when a uniform dispersion into a charge transporting layer is conducted in a solution state, it is preferable that the organic compound (A) is soluble in a solvent. In this point of view, the organic compound (A) preferably has a group as to enhance the compatibility with the charge transporting material and the solubility to a solvent. Examples of these groups include an alkyl group having 4 to 20 carbon atoms, an alkoxyl group having 4 to 20 carbon atoms, an aryl group having 6 to 20 carbon atoms taking part in a conjugated bond, an aryloxy group having 6 to 20 carbon atoms taking part in a conjugated bond, a heterocyclic compound group having 4 to 20 carbon atoms taking part in a conjugated bond and the like. It is preferable that at least one aryl group or heterocyclic compound group, which has at least one of the above group as a substituent, is contained in a molecule.
These groups are exemplified by the followings. The alkyl group having 4 to 20 carbon atoms includes butyl group, pentyl group, hexyl group, heptyl group, octyl group, decyl group and lauryl group and so on. Among them, pentyl group, hexyl group, heptyl group and octyl group are preferable.
The alkoxyl group having 4 to 20 carbon atoms includes butoxyl group, pentyloxy group, hexyloxy group, heptyloxy group, octyloxy group, decyloxy group, lauryloxy group and phenylpropyloxy group and so on. Among them, pentyloxy group, hexyloxy group, heptyloxy group, octyloxy group and phenylpropyloxy group are preferable.
The aryl group having 4 to 20 carbon atoms includes phenyl group, 4-C1-C12 alkoxyphenyl group, 4-C1-C12 alkylphenyl group, 1-naphtyl group and 2-naphtyl group and so on.
The aryloxyl group having 4 to 20 carbon atoms is exemplified by phenoxyl group.
The heterocyclic compound group having 4 to 20 carbon atoms includes 2-thienyl group, 2-pyrrolyl group, 2-furyl group, 2-,3- or 4-pyridyl group and so on.
The polymeric fluorescent substance contained in the light emitting layer of the polymer LED of the present invention is poly(arylene vinylene) or its derivative, and is the polymer containing the repeating unit represented by the above formula (1) in an amount of not less than 50% by mol based on the total repeating units. Depending on the structure of the repeating unit, the amount of the repeating unit represented by the formula (1) is preferably not less than 70% by mol based on the total repeating units. The polymeric fluorescent substance may contain a divalent aromatic compound group or its derivative, a divalent heterocyclic compound group or its derivative, or a divalent group combining thereof, etc. as the repeating unit other than the repeating unit represented by the formula (1). The repeating unit represented by the formula (1) and other repeating unit may be combined by a non-conjugated unit having an ether group, an ester group, an amide group, an imide group or the like. Alternatively, the non-conjugated portion may be contained in the repeating unit.
When the light emitting material is a polymeric fluorescent substance containing the repeating unit of the formula (1), Ar1of the formula (1) includes arylene group having 4 to 20 carbon atoms taking part in the conjugated bond, or heterocyclic compound group having 4 to 20 carbon atoms taking part in the conjugated bond, such as a divalent aromatic compound group or its derivative, a divalent heterocyclic compound group or its derivative, a divalent group combining thereof, or the like, shown in the following formulas (7) to (9). 
In the formulas, R27xcx9cR118 are independently a group selected from the group consisting of hydrogen, an alkyl group having 1 to 20 carbon atoms, an alkoxyl group having 1 to 20 carbon atoms, an alkylthio group having 1 to 20 carbon atoms; an aryl group having 6 to 18 carbon atoms, an aryloxyl group having 6 to 18 carbon atoms; a heterocyclic compound group having 4 to 14 carbon atoms.
Among these groups, a phenylene group, a substituted phenylene group, a biphenylene group, a substituted biphenylene group, a naphtalenediyl group, a substituted naphtalenediyl group, a anthracene-9,10-diyl group, a substituted anthracene-9,10-diyl group, a pyridine-2,5-diyl group, a substituted pyridine-2,5-diyl group, a thienylene group and a substituted thienylene group are preferable. More preferable are a phenylene group, a biphenylene group, a naphtalenediyl group, a pyridine-2,5-diyl group and a thienylene group.
In the case that R1 and R2 in the formula (1) are not a hydrogen or a cyano group, they are exemplified as follows.
The alkyl group having 1 to 20 carbon atoms are methyl group, ethyl group, propyl group, butyl group, pentyl group, hexyl group, heptyl group, octyl group, decyl group, lauryl group and so on. Among them, metyl group, ethyl group, pentyl group, hexyl group, heptyl group and octyl group are preferable.
The aryl group having 6 to 20 carbon atoms includes phenyl group, 4-C1-12 alkoxyphenyl group, 4-C1-12 alkylphenyl group, 1-naphtyl group and 2-naphtyl group and so on. The denotation of C1-12 means that 1 to 12 carbon atoms are contained in the alkoxy or alkyl group.
The heterocyclic compound group having 4 to 20 carbon atoms includes 2-thienyl group, 2-pyrrolyl group, 2-furyl group, 2-,3- or 4-pyridyl group and so on.
In view of the solvent solubility, Ar1 of the formula (1) has preferably one or more groups selected from the group consisting of alkyl, alkoxyl or alkylthio group having 4 to 20 carbon atoms, aryl or aryloxyl group having 6 to 20 carbon atoms, and heterocyclic compound group having 4 to 20 carbon atoms.
These substituent groups are exemplified by the followings. The alkyl group having 4 to 20 carbon atoms includes butyl group, pentyl group, hexyl group, heptyl group, octyl group, decyl group and lauryl group and so on. Among them, pentyl group, hexyl group, heptyl group and octyl group are preferable.
The alkoxyl group having 4 to 20 carbon atoms includes butoxyl group, pentyloxy group, hexyloxy group, heptyloxy group, octyloxy group, decyloxy group, lauryloxy group and phenylpropyloxy group and so on. Among them, pentyloxy group, hexyloxy group, heptyloxy group, octyloxy group and phenylpropyloxy group are preferable.
The alkylthio group having 4 to 20 carbon atoms includes butylthio group, pentylthio group, hexylthio group, heptylthio group, octylthio group, decylthio group, laurylthio group and so on. Among them, pentylthio group, hexylthio group, heptylthio group and octylthio group are preferable.
The aryl group having 4 to 20 carbon atoms includes phenyl group, 4-C1-12 alkoxyphenyl group, 4-C1-12 alkylphenyl group, 1-naphtyl group and 2-naphtyl group and so on.
The aryloxyl group having 4 to 20 carbon atoms is exemplified by phenoxyl group.
The heterocyclic compound group having 4 to 20 carbon atoms includes 2-thienyl group, 2-pyrrolyl group, 2-furyl group, 2-,3- or 4-pyridyl group and so on.
The number of these substituents varies depending on the molecular weight of the polymeric fluorescent substance and construction of the repeating unit. In order to obtain a polymeric fluorescent substance having high solubility, the number of these substituents is preferably at least one per molecular weight of 600.
The terminal group of the polymeric fluorescent substance is not specifically limited, but when the polymerizable group remains entirely, the light emitting properties and the lifetime of the devices are likely to deteriorate, therefore, it is preferably protected with a stable group. Those having a conjugated bond continued to conjugated structure of the main chain are more preferable. Examples thereof include the structure combined with an aryl group or a heterocyclic compound group through a vinylene group.
Specific examples are phenyl group, pyridyl group, naphtyl group, anthryl group, pyrenyl group, perylenyl group, phenynthrenyl group, thienyl group, furyl group, oxadiazolyl group, benzoxazolyl group, fluorenyl group, quinolyl group, quinoxalyl group, and derivative thereof. Among them, phenyl group, 1-naphtyl group, 9-anthryl group, 2-pyridyl group, 2-thienyl group, 1-pyrenyl group, 2-fluorenyl group, 2-quinolyl group and derivative thereof are preferable. More preferable are 1-naphtyl group, 9-anthryl group, 1-pyrenyl group and 2-fluorenyl group.
A synthesizing method of the polymeric fluorescent substance is not specifically limited, and examples thereof include a method described in JP-A-5-202355. That is, examples thereof include polymerization by Witting reaction between a dialdehyde compound and a diphosponium salt compound, polycondensation by dehydrohalogenation method of a compound having two halogenated methyl groups, polycondensation by sulfonium salt decomposition method of a compound having two sulfonium salt groups, polymerization by Knoevenagel reaction between a dialdehyde compound and a diacetonitrile compound and the like.
The polymeric fluorescent substance may be a random, block or graft copolymer, or a polymer having an intermediate structure of them, for example, a partially block type random copolymer. In view of obtaining a polymeric fluorescent substance having high quantum yield of fluorescence, a partially block type random copolymer, and a block or graft copolymer is preferable to a completely random copolymer. The case of having branches in the main chain and containing three or more terminals is also included.
Since light emission from a thin film is utilized, the polymeric fluorescent substance having luminescence in the solid state is preferably used.
Examples of a good solvent for the polymeric fluorescent substance include chloroform, methylene chloride, dichloroethane, tetrahydrofuran, toluene, xylene, mesitylene, decalin, n-butylbenzene and the like. The polymeric fluorescent substance can be usually dissolved in a solvent in an amount of not less than 0.1% by weight, although the amount varies depending on the structure or molecular weight of the polymeric fluorescent substance.
The molecular weight of the polymeric fluorescent substance is preferably within the range from 103 to 107 in terms of polystyrene, and the polymerization degree varies depending on the structure of repeating units and their proportion. In view of the film forming property, the total number of the repeating unit is suitably within the range from 10 to 10000, more suitably from 10 to 3000, and preferably from 20 to 2000.
When these polymeric fluorescent substances are used as the light emitting material of the polymeric LED, since the purity have an influence on light emitting characteristics, the polymeric fluorescent substance is preferably subjected to a purification treatment such as purification by means of reprecipitation, separation by means of chromatography or the like, after synthesis.
On producing the polymeric LED, in the case of film forming from a solution using these polymeric fluorescent substances, which are soluble in an organic solvent, the solvent of this solution is only removed by drying after coating. Also, in the case of mixing a charge transporting material and light emitting material, the same method can be applied, therefore, it is very advantageous on producing. As a method of forming a film forming from a solution, coating methods such as spin coating method, casting method, micro gravure coating method, gravure coating method, bar coating method, roll coating method, wire bar coating method, dipping method, spray coating method, screen printing method, flexographic printing method, offset printing method or the like can be used.
As the light emitting layer, for example, a light emitting material other than the polymeric fluorescent substance may be used in combination.
As the light emitting material, well-known materials can be used. As the low-molecular-weight compound, for example, the light emitting material includes pigments such as naphthalene derivative, anthracene and its derivative, perylene and its derivative; dyes such as polymethine, xanthene, coumarin, cyanine and the like; and metal complex of 8-hydroxyquinoline and its derivative, aromatic amine, tetraphenylcyclopentadiene and its derivative, and tetraphenylbutadiene and its derivative and the like.
Specific examples thereof include well-known light emitting materials such as those described in JP-A-57-51781 and JP-A-59-194393.
When the polymeric LED of the present invention has at least one hole transporting layer, the hole transporting material used is not specifically limited, and examples thereof include,
(a) the hole transporting material having a carbazole ring or its derivative at the side chain such as polyvinyl carbazole and its derivative
(b) polysilane and its derivative
(c) the hole transporting material having an aromatic amine compound group at the side chain or the main chain such as polysiloxane derivative having aromatic amine in the side chain or the main chain, polyaniline and its derivative
(d) pyrazoline derivative, arylamine derivative, stilbene derivative, triphenyldiamine derivative
(e) the conjugated polymer such as polythiophene and its derivative, poly(p-phenylenevinylene) and its derivative, poly(2,5-thienylenevinylene) and its derivative and the like.
Specific examples of the hole transporting material include those described in JP-A-63-70257, JP-A-63-175860, JP-A-2-135359, JP-A-2-135361, JP-A-2-209988, JP-A-3-37992, JP-A-3-152184 and the like.
Among them, the hole transporting material used in the hole transporting layer is preferably the polymeric hole transporting material such as polyvinyl carbazole and its derivative, polysilane and its derivative, polysiloxane derivative having aromatic amine compound group in the side chain or the main chain, polyaniline and its derivative, polythiophene and its derivative, poly(p-phenylenevinylene) and its derivative, poly(2,5-thienylenevinylene) and its derivative and the like, and more preferably polyvinyl carbazole and its derivative, polysilane and its derivative, polysiloxane derivative having aromatic amine compound group in the side chain or the main chain. In the case of using the low-molecular-weight hole transporting material, it is preferably used by dispersing in a polymer binder.
Polyvinyl carbazole and its derivative can be obtained, for example, by cation polymerization or radical polymerization from vinyl monomers.
Examples of the polysilane and its derivative include compounds such as those described in Chem. Rev. Vol.89, page 1359 (1989) and GP2300196. As the synthesizing method, the method described in them can be used. Among them, a Kipping method is preferably used.
Polysiloxane and its derivative, since the siloxane skeleton structure has little hole transporting properties, those having the structure of the above low-molecular-weight hole transporting material in the side chain or the main chain is appropriately used. Examples thereof include those having aromatic amine having the hole transporting properties at the side chain or main chain.
The method of forming a film of the hole transport layer is not limited. As the low-molecular-weight hole transporting material, examples thereof include a method of forming a film from a mixed solution with a polymer binder. In the case of polymeric hole transporting material, examples include a method of forming a film from a solution.
The solvent used for a film forming from a solution is not specifically limited, as far as it dissolves the hole transporting material. Examples of the solvent include chlorine solvents such as chloroform, methylene chloride, dichloroethane and the like; ether solvents such as tetrahydrofuran and the like; aromatic hydrocarbon solvents such as toluene, xylene and the like; ketone solvents such as acetone, methyl ethyl ketone and the like; ester solvents such as ethyl acetate, butyl acetate, ethylcellsolve acetate and the like.
As a method of forming a film forming from a solution, coating methods such as spin coating method, casting method, micro gravure coating method, gravure coating method, bar coating method, roll coating method, wire bar coating method, dipping method, spray coating method, screen printing method, flexographic printing method, offset printing method or the like can be used.
As the polymeric binder to be mixed, those which do not extremely inhibit charge transport are preferable. Those whose absorption to visible light is not strong are preferably used. Examples of the polymer binder include polycarbonate, polyacrylate, polymethyl acrylate, polymethyl methacrylate, polystyrene, polyvinyl chloride, polysiloxane and the like.
In the present invention, when the polymer LED has the electron transport layer, as the electron transporting material used, well-known materials can be used. Examples thereof include oxadiazole derivative, anthraquinodimethane and its derivative, benzoquinone and its derivative, naphthoquinone and its derivative, anthraquinone and its derivative, tetracyanoanthraquinodimethane and its derivative, fluorenone derivative, diphenyldicyanoethylene and its derivative, diphenoquinone derivative, metal complex of 8-hydroxyquinoline and its derivative and the like.
Specific examples thereof include those described in JP-A-63-70257, JP-A-63-175860, JP-A-2-135359, JP-A-2-135361, JP-A-2-209988, JP-A-3-37992 and JP-A-3-152184.
Among them, oxadiazole derivative, benzoquinone and its derivative, anthraquinone and its derivative, and metal complex of 8-hydroxyquinoline and its derivative are preferable, 2-(4-biphenylyl)-5-(4-t-butylphenyl)-1,3,4-oxadiazole, benzoquinone, anthraquinone and tris(8-quinolinol)aluminum are more preferable.
The method of forming a film of the electron transport layer is not specifically limited. In case of the low-molecular-weight electron transporting material, there can be used vacuum deposition method from the powder state or method by film forming from the solution or molten state. In case of the polymeric electron transporting material, there can be used a method by film forming from the solution or molten state. In case of forming the film from the solution or molten state, the polymer binder may be used in combination.
The solvent used for film forming from the solution is not limited, as far as it can dissolve the electron transporting material and/or polymer binder. Examples of the solvent include chlorine solvents such as chloroform, methylene chloride, dichloroethane and the like; ether solvents such as tetrahydrofuran and the like; aromatic hydrocarbon solvents such as toluene, xylene and the like ketone solvents such as acetone, methyl ethyl ketone and the like; ester solvent such as ethyl acetate, butyl acetate, ethylcellsolve acetate and the like.
As a method of forming a film forming from a solution or molten state, coating methods such as spin coating method, casting method, micro gravure coating method, gravure coating method, bar coating method, roll coating method, wire bar coating method, dipping method, spray coating method, screen printing method, flexographic printing method, offset printing method or the like can be used.
As the polymer binder to be mixed, those which do not extremely inhibit charge transport are preferable. Those whose absorption to visible light is not strong are preferably used. Examples of the polymer binder include poly(N-vinylcarbazole), polyaniline and its derivative, polythiophene and its derivative, poly(p-phenylenevinylene) and its derivative, poly(2,5-thienylenevinylene) and its derivative, polycarbonate, polyacrylate, polymethyl acrylate, polymethyl methacrylate, polystyrene, polyvinyl chloride, polysiloxane and the like.
In the present invention, as the transparent or semitransparent metal of the anode, there can be used conductive material oxide films, semitransparent metal thin films and the like. Specifically, indium-tin oxide (ITO), zinc oxide(ZnO), films (e.g. NESA) made of conductive glasses such as tin oxide(SnO2), and the like, Au, Pt, Ag, Cu and the like are used. ITO, ZnO and SnO2 are preferable. Examples of the production method include vacuum deposition method, sputtering method, ion plating method, plating method and the like. As the anode, an organic transparent conductive film such as polyaniline and its derivative, polythiophene and its derivative and the like may also be used.
AS the material using in the cathode of the present invention, it is preferable to have small work function. For example, there can be used Al, In, Mg, Ca, Li, Mgxe2x80x94Ag alloy, Mgxe2x80x94In alloy, Mgxe2x80x94Al alloy, Inxe2x80x94Ag alloy, Alxe2x80x94Li alloy, Lixe2x80x94Mg alloy, Lixe2x80x94In alloy, Caxe2x80x94Al alloy, graphite, praphite intercalation compound, and the like.
As the method of producing the cathode, there can be used vacuum deposition method, sputtering method or laminate method by heat-pressing thin metal films and the like. After producing the anode, a protecting layer for protecting the polymeric LED may also be provided.
The following Examples further illustrate the present invention in detail but are not to be construed to limit the scope thereof.